ELisp: Define Function

Basic function definition is of the form:

(defun function_name (param1 param2 etc) doc_string_optional body)

(defun ff ()
  "print yay"
  (message "Yay!"))

(defun gg (x)
  "add two"
  (+ x 2))

(defun ff (x y)
  "add x and y"
  (+ x y))

When a function is called, the last expression in the function's definition body is returned. (there's no “return statement”.)

Define a Command

To define a command, add (interactive) right after the docstring.

• ELisp: How to Write a Command

Reference

Defining Functions (ELISP Manual)